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Acta Metall Sin  2019, Vol. 55 Issue (2): 181-190    DOI: 10.11900/0412.1961.2018.00187
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The Influence of Rolling Process on the Microstructure, Texture and Magnetic Properties of Low Grades Non-Oriented Electrical Steel After Phase Transformation Annealing
Chen GU, Ping YANG(), Weimin MAO
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
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Chen GU, Ping YANG, Weimin MAO. The Influence of Rolling Process on the Microstructure, Texture and Magnetic Properties of Low Grades Non-Oriented Electrical Steel After Phase Transformation Annealing. Acta Metall Sin, 2019, 55(2): 181-190.

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Abstract  

Non-oriented electrical steel sheets are important metallic functional materials for the iron cores in transformers and electrical motors, which require the performance characteristics of low iron loss and high magnetic induction. The magnetic properties of electrical steel critically depend on the microstructure and the occurring texture components. In addition, alloy elements can affect the magnetic properties by altering the electrical resistivity, microstructure and texture. At present, the quality of commercial non-oriented electrical steels are mainly optimized by the control of deformation, recrystallization parameters and chemical composition. And the microstructure, texture and magnetic properties are significantly influenced by the rolling process before recrystallization annealing. The favorite {100} texture in such condition takes at maximum only about 20% in volume fraction. In contrast, phase transformation combined with deformation can lead to nearly 80% volume fraction of {100}-oriented grains. In this work, the influence of rolling process on the microstructure, texture and magnetic properties of low grades non-oriented electrical steel after phase transformation annealing was studied by means of EBSD, XRD and magnetism measuring techniques. The starting material is a columnar-grained industrial low grades electrical steel cast slab. Five different initial microstructures are obtained after different rolling processes, the α→γ→α phase transformation annealing of samples is conducted in a tube furnace under H2 atmosphere. The results show that phase transformation annealing can significantly coarsen grains and reduce the iron loss of non-oriented electrical steels compared with traditional recrystallization annealing. And the phase transformation texture is influenced by texture memory. Compared with hot rolling-cold rolling process, more {100}-oriented grains are obtained and the magnetic properties of non-oriented electrical steels are improved significantly after phase transformation in the directly cold rolling process. The proportion of non-{111} oriented grains increases and more initial {100}-oriented grains are retained after phase transformation in the process with lower hot rolling temperature, which improve the magnetic properties of final sample. In addition, the presence of P and Al elements in commercial electrical steels may affect the microstructure, texture and magnetic properties of non-oriented electrical steels due to segregation and oxidation after phase transformation.
Key words:  non-oriented electrical steel      rolling process      texture memory      phase transformation      chemical element     
Received:  10 May 2018     
ZTFLH:  TG111  
Fund: Supported by National Natural Science Foundation of China (No.51771024)
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Chen GU
Ping YANG
Weimin MAO

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https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00187     OR     https://www.ams.org.cn/EN/Y2019/V55/I2/181

Processing route Hot rolling Cold rolling
A Holding at 1150 ℃ for 30 min, hot rolling by 3 passes and air cooling, 2 mm thickness in hot band, 80% rolling reduction Cold rolling to 0.35 mm (82.5%)
B
 Holding at 1150 ℃ for 30 min, hot rolling to 4 mm, then reheating at 1150 ℃ for 5 min followed by 2 passes to 2 mm thickness, air cooling, 50% rolling reduction Cold rolling to 0.35 mm (82.5%)
C The same as route A except heating at 1100 ℃, air cooling, 80% rolling reduction, 2 mm thickness Cold rolling to 0.35 mm (82.5%)
D The same as route C, water cooling Cold rolling to 0.35 mm (82.5%)
E - Direct cold rolling to 0.35 mm (82.5%)
Table 1  The rolling process before final transformation treatment
Fig.1  Macrostructure and EBSD data of the cast slab (φ1, ?, and φ2 are the Euler angles, which form a three-dimensional orientation space; RD, TD and ND represent rolling direction, transverse direction and normal direction of the sheets, respectively)
(a) macrostructure
(b) orientation distribution function (ODF) at φ2=45° section
(c) {200} pole figure
(d) IPF-X (projection of the grain orientations that are parallel to RD in the crystal coordinate system) map (IPF—inverse pole figure)
(e) Kikuchi band quality map
Fig.2  EBSD data of annealed sample for commercial 1300 grade non-oriented electrical steel
(a) IPF-Z (projection of the grain orientations that are parallel to ND in the crystal coordinate system) map for rolling plane
(b) {200} pole figure
(c) ODF at φ2=45° section
Fig.3  IPF-Z maps (a~d) and ODFs at φ2=45° section (e~h) for through-thickness cross section of hot rolling samples in processes A (a, e), B (b, f), C (c, g) and D (d, h), respectively
Fig.4  ODFs at φ2=45° section of texture on the surface of cold rolled samples in the processes A (a), B (b), C (c), D (d) and E (e), respectively
Fig.5  IPF-Z maps (a~e) and ODFs (φ2=45°) (f~j) for through thickness cross section of annealed samples in the rolling processes A (a, f), B (b, g), C (c, h), D (d, i) and E (e, j), respectively
Fig.6  Average grain sizes of annealed samples in different rolling processes
Fig.7  Iron loss (P1.5) (a) and magnetic induction (B50) (b) of transformation annealed samples in different rolling processes
Fig.8  Glow discharge spectrum (GDS) data profiles for the annealed sample in process C
(a) O, Si, Al, P profile after annealing within 2.0 μm from the surface
(b) Al, P profile after annealing within 1.0 μm from the surface
(c) P profiles after annealing within 1.0 μm from the surface
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